Why mp3 file converted by ffmpeg is not playable on IOS?

Question

PHP

The site is recording a comment using the GetUserMedia API. Next, the file is sent to the server and converted to mp3 using the ffmpeg utility.
Everywhere everything works fine, but not on IOS.

If you download a file from the player. then he seems to have only 1 second of recording. Everything works fine on other OSes.
What could be the problem?

The code is quite normal:

shell_exec('ffmpeg -y -i '.$temp_name.' '.$file.'');